Elastic wave device

ABSTRACT

An elastic wave device includes a piezoelectric substrate, and elastic wave elements on the piezoelectric substrate and including IDT electrodes, respectively. The IDT electrode of a first of the elastic wave elements includes first and second busbars, and the IDT electrode of a second of the elastic wave elements includes third and fourth busbars. The second busbar and the third busbar extend parallel or substantially parallel to each other, and are spaced by a gap in a direction perpendicular or substantially perpendicular to an elastic-wave propagating direction. Each of the second and third busbars includes first and second electrode layers at least a portion of which is laminated on the first electrode layer. The second electrode layer of the second busbar is cut in at least one location in a direction crossing the elastic-wave propagating direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2015-254157 filed on Dec. 25, 2015. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an elastic wave device.

2. Description of the Related Art

Elastic wave devices have been widely used in, for example, filters ofcellular phones. Japanese Unexamined Patent Application Publication No.2002-100952 discloses one example of an elastic wave device includingIDT (interdigital transducer) electrodes. Each of busbars of the IDTelectrodes includes a lower layer wiring and an upper layer wiringlaminated on the lower layer wiring.

Recently, in order to satisfy a demand for further size reduction of theelastic wave device, the distance between adjacent busbars of the IDTelectrodes has gradually decreased due to design of arranging elasticwave resonators closer to each other in a direction perpendicular to anelastic-wave propagating direction. On the other hand, in a ladderfilter, for example, a size of the IDT electrode of the elastic waveresonator taken along the elastic-wave propagating direction hasincreased to improve filter characteristics, and hence a length of thebusbar has also increased. Accordingly, when the elastic wave resonatorsincluding the IDT electrodes, which have the busbars of two-layerstructure and which are horizontally elongated as in Japanese UnexaminedPatent Application Publication No. 2002-100952, are arranged close toeach other, a formation failure or defect in the busbars is likely tooccur, thus resulting in a possibility that short-circuiting may occurbetween the adjacent busbars. For that reason, it has been difficult toarrange the IDT electrodes in a sufficiently close relation, and toprovide satisfactory size reduction of the elastic wave device.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a reduced sizeelastic wave device in which a formation failure or defect in busbars isless likely to occur in a region where IDT electrodes are adjacent to orin a vicinity of each other.

According to a preferred embodiment of the present invention, an elasticwave device includes a piezoelectric substrate, and a plurality ofelastic wave elements provided on the piezoelectric substrate andincluding IDT electrodes, respectively. The plurality of elastic waveelements includes a first elastic wave element and a second elastic waveelement. The IDT electrode of the first elastic wave element includesfirst and second busbars that oppose each other, and the IDT electrodeof the second elastic wave element includes third and fourth busbarsthat oppose each other. The second busbar and the third busbar extendparallel or substantially parallel to each other and a gap is includedbetween the second busbar and the third busbar in a directionperpendicular or substantially perpendicular to an elastic-wavepropagating direction. Each of the second and third busbars includes afirst electrode layer and a second electrode layer, and at least aportion of the second electrode layer is laminated on the firstelectrode layer. The second electrode layer of the second busbar is cutin at least one location in a direction crossing the elastic-wavepropagating direction.

In a preferred embodiment of the present invention, the second electrodelayer of the second busbar is cut in a direction perpendicular orsubstantially perpendicular to the elastic-wave propagating direction.

In another preferred embodiment of the present invention, the secondelectrode layer of the third busbar is cut in at least one location in adirection crossing the elastic-wave propagating direction. Accordingly,a failure or defect in the second and third busbars is less likely tooccur.

In another preferred embodiment of the present invention, the secondelectrode layer of the third busbar is cut in a direction perpendicularor substantially perpendicular to the elastic-wave propagatingdirection.

In another preferred embodiment of the present invention, the secondelectrode layer of the third busbar is cut in a portion corresponding toan extension from a cut portion of the second electrode layer of thesecond busbar, the extension extending in a direction in which thesecond electrode layer of the second busbar is cut.

In another preferred embodiment of the present invention, the pluralityof elastic wave elements includes one or more serial arm resonators anda plurality of parallel arm resonators, and the first and second elasticwave elements are included in the plurality of parallel arm resonators.Accordingly, a formation failure or defect in the busbars of theparallel arm resonators is less likely to occur even when lengths of theparallel arm resonators in the elastic-wave propagating direction areincreased. As a result, filter characteristics of the elastic wavedevice are able to be improved, and the size of the elastic wave deviceis able to be further reduced.

In another preferred embodiment of the present invention, the elasticwave device further includes a first band pass filter and a second bandpass filter. A pass band of the second band pass filter is differentfrom a pass band of the first band pass filter, and the first band passfilter includes at least one of the first and second elastic waveelements.

In another preferred embodiment of the present invention, the first bandpass filter includes one of the first and second elastic wave elements,and the second band pass filter includes the other of the first andsecond elastic wave elements. Accordingly, a distance between the firstband pass filter and the second band pass filter is able to be furtherreduced. As a result, the size of the elastic wave device is able to befurther reduced.

With the elastic wave device according to the preferred embodiments ofthe present invention, a formation failure or defect in the busbars isless likely to occur in a region where the IDT electrodes are adjacentto or in a vicinity of each other, and a reduction in size is able to beprovided.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments of thepresent invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an elastic wave device according to afirst preferred embodiment of the present invention.

FIG. 2 is a circuit diagram of the elastic wave device according to thefirst preferred embodiment of the present invention.

FIG. 3 is a plan view showing an electrode arrangement of a serial armresonator in the first preferred embodiment of the present invention.

FIG. 4 is a plan view showing electrode arrangements of first and secondlongitudinally-coupled resonator-type elastic wave filters in the firstpreferred embodiment of the present invention.

FIG. 5 is an enlarged schematic plan view of the elastic wave deviceaccording to the first preferred embodiment of the present invention.

FIG. 6 is a schematic plan view of a portion corresponding to first andsecond elastic wave elements, the view being referenced to explain amanufacturing process of the elastic wave device according to the firstpreferred embodiment of the present invention.

FIG. 7 is a schematic plan view of the portion corresponding to thefirst and second elastic wave elements, the view being referenced toexplain the manufacturing process of the elastic wave device accordingto the first preferred embodiment of the present invention.

FIG. 8 is a schematic plan view of the portion corresponding to thefirst and second elastic wave elements, the view being referenced toexplain the manufacturing process of the elastic wave device accordingto the first preferred embodiment of the present invention.

FIG. 9 is a graph plotting insertion losses of respective first bandpass filters in the first preferred embodiment of the present inventionand a comparative example.

FIG. 10 is a schematic plan view of an elastic wave device according toa second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The features of the present invention will be clarified through thefollowing description of specific preferred embodiments of the presentinvention with reference to the drawings.

It is to be noted that the preferred embodiments disclosed in thisspecification are merely illustrative, and that components orconfigurations in the different preferred embodiments may be partlyexchanged or combined with each other.

First Preferred Embodiment

FIG. 1 is a schematic plan view of an elastic wave device according to afirst preferred embodiment of the present invention. FIG. 2 is a circuitdiagram of the elastic wave device according to the first preferredembodiment. In FIG. 1, elastic wave resonators andlongitudinally-coupled resonator-type elastic wave filters arerepresented by two diagonal lines in a polygon. The features andelements shown in FIG. 1 are similarly applied to FIGS. 5, 6, 8 and 10,which are described below.

The elastic wave device according to the first preferred embodiment is aduplexer 1 shown in FIG. 1. The duplexer 1 includes a piezoelectricsubstrate 2. The piezoelectric substrate 2 includes, for example, apiezoelectric single crystal such as LiNbO₃ or LiTaO₃, or an appropriatepiezoelectric ceramic.

The duplexer 1 includes a first band pass filter 3 a and a second bandpass filter 3 b with a pass band different from a pass band of the firstband pass filter 3 a. Both of the band pass filters 3 a and 3 b areprovided on the piezoelectric substrate 2. The first band pass filter 3a is a transmission filter, and the second band pass filter 3 b is areception filter.

The duplexer 1 is provided on the piezoelectric substrate 2 and includesan antenna terminal 5 that is connected to an antenna. The first andsecond band pass filters 3 a and 3 b are connected in common to theantenna terminal 5.

The first band pass filter 3 a corresponds to, for example, an elasticwave device according to a preferred embodiment of the presentinvention.

Each of the first and second band pass filters 3 a and 3 b includes aplurality of elastic wave elements. Each of the plurality of elasticwave elements includes an IDT electrode. In more detail, as shown inFIG. 2, the first band pass filter 3 a includes, as the plurality ofelastic wave elements, serial arm resonators S1 to S4 and parallel armresonators P1 to P3. The first band pass filter 3 a is a ladder filter.

FIG. 3 is a plan view showing an electrode arrangement of the serial armresonator S1 in the first preferred embodiment.

The serial arm resonator S1 includes an IDT electrode 10A provided onthe piezoelectric substrate 2. Reflectors 11A and 11A are located onboth sides of the IDT electrode 10A in an elastic-wave propagatingdirection. Similarly, each of the other serial arm resonators S2 to S4,the parallel arm resonators P1 to P3, and later-described elastic waveresonators S11 and P11, shown in FIG. 2, includes an IDT electrode and apair of reflectors.

The second band pass filter 3 b includes, as the plurality of elasticwave elements, first and second longitudinally-coupled resonator-typeelastic wave filters 7 a and 7 b, and the elastic wave resonators S11and P11.

FIG. 4 is a plan view showing electrode arrangements of the first andsecond longitudinally-coupled resonator-type elastic wave filters in thefirst preferred embodiment.

The first longitudinally-coupled resonator-type elastic wave filter 7 aincludes IDT electrodes 10Ba to 10Bc. Reflectors 11B and 11B are locatedon both sides of the IDT electrodes 10Ba to 10Bc in the elastic-wavepropagating direction. The second longitudinally-coupled resonator-typeelastic wave filter 7 b includes IDT electrodes 10Ca to 10Cc. Reflectors11C and 11C are located on both sides of the IDT electrodes 10Ca to 10Ccin the elastic-wave propagating direction.

FIG. 5 is an enlarged schematic plan view of the elastic wave deviceaccording to the first preferred embodiment.

As shown in FIG. 5, the parallel arm resonator P1 in the first band passfilter 3 a corresponds to a first elastic wave element. The IDTelectrode of the parallel arm resonator P1 includes first and secondbusbars 9 a and 9 b that are opposed to each other. On the other hand,the serial arm resonator S1 corresponds to a second elastic waveelement. The IDT electrode of the serial arm resonator S1 includes thirdand fourth busbars 9 c and 9 d that are opposed to each other.

The first to fourth busbars 9 a to 9 d each extend in a lengthwisedirection. The second busbar 9 b and the third busbar 9 c extendparallel or substantially parallel to each other. In the first preferredembodiment, the lengthwise direction is a direction parallel orsubstantially parallel to the elastic-wave propagating direction in eachof the parallel arm resonator P1 and the serial arm resonator S1. A gapis included between the second busbar 9 b and the third busbar 9 c in adirection perpendicular or substantially perpendicular to the lengthwisedirection.

Each of the second and third busbars 9 b and 9 c includes a firstelectrode layer and a second electrode layer laminated on the firstelectrode layer. In the first preferred embodiment, each of the firstand fourth busbars 9 a and 9 d also includes a first electrode layer anda second electrode layer laminated on the first electrode layer. Anelectrical resistance is able to be reduced with the two-layer structureof the first electrode layer and the second electrode layer. Accordingto a modification of the first preferred embodiment, each of at leastthe second and third busbars 9 b and 9 c includes the first and secondelectrode layers. Furthermore, according to a modification of the firstpreferred embodiment, the second electrode layer is partially laminatedon the first electrode layer.

In the first and second band pass filters, for example, each of thebusbars of the IDT electrodes in all the elastic wave elementspreferably includes electrode layers corresponding to theabove-described first and second electrode layers. Accordingly, theelectrical resistance is able to be further reduced.

The second busbar 9 b includes a cut portion 9B where the secondelectrode layer is cut in a direction perpendicular or substantiallyperpendicular to the lengthwise direction of the second busbar 9 b to bepartially separated. The first electrode layer of the second busbar 9 bis exposed in the cut portion 9B.

Similarly, the third busbar 9 c includes a cut portion 9C where thesecond electrode layer is cut in a direction perpendicular orsubstantially perpendicular to the lengthwise direction of the thirdbusbar 9 c to be partially separated. In more detail, the secondelectrode layer of the third busbar 9 c is cut in a portioncorresponding to an extension from the cut portion 9B of the secondbusbar 9 b, the extension extending in the direction in which the secondelectrode layer of the second busbar 9 b is cut. The first electrodelayer of the third busbar 9 c is exposed in the cut portion 9C.

The first preferred embodiment includes the feature of the secondelectrode layer of the second busbar 9 b and the second electrode layerof the third busbar 9 c each being cut to be partially separated, asdescribed above. Accordingly, a formation failure or defect in thebusbars is less likely to occur in a region where the IDT electrodes areadjacent to or in a vicinity of each other. In addition, a reduction insize of the duplexer 1 is able to be provided. The above features aredescribed below with a detailed description of the duplexer 1 and anon-limiting example of a method of manufacturing the duplexer 1.

As shown in FIG. 2, the first band pass filter 3 a includes an inputterminal 4. The serial arm resonators S1 to S4 are connected in seriesbetween the input terminal 4 and the antenna terminal 5.

The parallel arm resonator P1 is connected between a ground potentialand a junction of the serial arm resonator S1 closest to the inputterminal 4 and the serial arm resonator S2. The parallel arm resonatorP2 is connected between the ground potential and a junction of theserial arm resonator S2 and the serial arm resonator S3. The parallelarm resonator P3 is connected between the ground potential and ajunction of the serial arm resonator S3 and the serial arm resonator S4.However, the circuit configuration of the first band pass filter 3 a isnot limited to the particular configuration described above.

The second band pass filter 3 b includes an output terminal 6. The firstand second longitudinally-coupled resonator-type elastic wave filters 7a and 7 b are connected in series between the antenna terminal 5 and theoutput terminal 6. The elastic wave resonator S11 for characteristicadjustment is connected between the antenna terminal 5 and the firstlongitudinally-coupled resonator-type elastic wave filter 7 a. Theelastic wave resonator P11 for characteristic adjustment is connectedbetween a junction of the antenna terminal 5 and the elastic waveresonator S11 for characteristic adjustment and the ground potential.However, the circuit configuration of the second band pass filter 3 b isnot limited to the particular configuration described above.

As shown in FIG. 1, a plurality of ground terminals 8 is located on thepiezoelectric substrate 2. The plurality of ground terminals 8 isconnected to a ground potential.

One non-limiting example of a manufacturing process of the duplexer 1,that is, the elastic wave device according to the first preferredembodiment, is described below.

FIG. 6 is a schematic plan view of a portion corresponding to the firstand second elastic wave elements, the view being referenced to explainthe manufacturing process of the elastic wave device according to thefirst preferred embodiment. FIG. 7 is a schematic plan view of theportion corresponding to the first and second elastic wave elements, theview being referenced to explain the manufacturing process of theelastic wave device according to the first preferred embodiment. FIG. 8is a schematic plan view of the portion corresponding to the first andsecond elastic wave elements, the view being referenced to explain themanufacturing process of the elastic wave device according to the firstpreferred embodiment. In FIGS. 6 to 8, electrode arrangements for theother elastic wave elements on the piezoelectric substrate than thefirst and second elastic wave elements are omitted. Moreover, asdescribed above, the first and second elastic wave elements are theparallel arm resonator P1 and the serial arm resonator S1, respectively,shown in FIG. 5. In FIG. 7, a region where a later-described resistpattern is provided is indicated by hatching.

As shown in FIG. 6, the piezoelectric substrate 2 is prepared. Then, ametal film is provided on the piezoelectric substrate 2. The metal filmis able to be provided by, for example, sputtering or chemical vapordeposition (CVD). Then, a first wiring layer 12 is provided bypatterning the metal film with photolithography. The first wiring layer12 includes electrodes in respective first layers of the IDT electrodesand the reflectors. Respective first electrode layers 9 a 1 to 9 d 1 ofthe above-described first to fourth busbars are provided through thesteps described above.

Next, as shown in FIG. 7, a resist pattern 13 is provided on thepiezoelectric substrate 2 to cover a portion of the first wiring layer12. The resist pattern 13 covers individual electrode fingers of the IDTelectrodes. The resist pattern 13 includes portions opened at positionsabove the first electrode layers 9 a 1 to 9 d 1 of the first to fourthbusbars. In a later-described step, respective second electrode layersof the first to fourth busbars are provided in the opened regions.

A thickness of the resist pattern 13 is preferably larger than athickness of the first wiring layer 12 shown in FIG. 6. Accordingly,thicknesses of respective second electrode layers of the first to fourthbusbars are able to be increased, and electrical resistances are able tobe further reduced.

The resist pattern 13 includes a narrow width portion 13 a that ispositioned between the first electrode layer 9 b 1 of the second busbarand the first electrode layer 9 c 1 of the third busbar, and thatextends along the first electrode layers 9 b 1 and 9 c 1. The narrowwidth portion 13 a extends over an entire length of a region where thefirst electrode layers 9 b 1 and 9 c 1 of the second and third busbarsare positioned in an opposing relation. A width of the narrow widthportion 13 a is equal or substantially equal to a size of the narrowwidth portion 13 a in a direction crossing the direction in which thenarrow width portion 13 a extends. As the distance between the secondbusbar and the third busbar shortens, the width of the narrow widthportion 13 a is reduced.

In a step shown in FIG. 7, the resist pattern 13 includes reinforcementportions 13 b and 13 c that reinforce the narrow width portion 13 a. Inmore detail, the reinforcement portion 13 b is provided on the firstelectrode layer 9 b 1 of the second busbar. The reinforcement portion 13b connects the narrow width portion 13 a and the other portion of theresist pattern 13. Similarly, the reinforcement portion 13 c is providedon the first electrode layer 9 c 1 of the third busbar. Thereinforcement portion 13 c also connects the narrow width portion 13 aand the other portion of the resist pattern 13. As described below, thesecond electrode layer of the second busbar and the second electrodelayer of the third busbar are cut in regions corresponding to thereinforcement portions 13 b and 13 c, respectively.

A failure or defect, such as a positional deviation, in the narrow widthportion 13 a is more likely to occur as the width of the narrow widthportion 13 a reduces and the thickness thereof increases. Furthermore,the failure or defect in the narrow width portion 13 a is more likely tooccur as the length of the narrow width portion 13 a increases. In viewof the above-described unique structure, the narrow width portion 13 ais reinforced by the reinforcement portions 13 b and 13 c. With thepresence of the reinforcement portions 13 b and 13 c, the failure ordefect in the narrow width portion 13 a is significantly reduced orprevented even when the distance between the second busbar 9 b and thethird busbar 9 c is shortened. In addition, the failure or defect in thenarrow width portion 13 a is significantly reduced or prevented evenwhen the lengths of the second and third busbars are increased. As aresult, a failure or defect in the second and third busbars, which areprovided by patterning the resist pattern 13, is significantly reducedor prevented.

Thus, the failure or defect in the second and third busbars issignificantly reduced or prevented by providing the reinforcementportions 13 b and 13 c and cutting each of the second electrode layersof the second and third busbars to be partially separated as describedabove.

According to a modification of the first preferred embodiment, at leastone of the reinforcement portions 13 b and 13 c is provided at onelocation. Accordingly, the positional deviation of the narrow widthportion 13 a is less likely to occur. As an alternative, thereinforcement portion 13 b or 13 c may be provided in plural.

Next, a metal film is provided on the piezoelectric substrate 2 in botha portion covered with the resist pattern 13 and a portion not coveredwith the resist pattern 13. The resist pattern 13 is then peeled off. Asa result, the second electrode layers 9 a 2 to 9 d 2 of the first tofourth busbars 9 a to 9 d are provided as shown in FIG. 8.

In the step of peeling off the resist pattern 13 as described above, themetal films on the reinforcement portions 13 b and 13 c of the resistpattern 13, shown in FIG. 7, are removed together. Thus, the cutportions 9B and 9C of the second and third busbars 9 b and 9 c areformed. As a result, the parallel arm resonator P1 and the serial armresonator S1 are formed. Through the steps described above, the otherelastic wave elements, including the elastic wave resonators and thelongitudinally-coupled resonator-type elastic wave filters, are alsoformed at the same or substantially the same time.

As described above, the positional deviation of the narrow width portion13 a is less likely to occur even when the width of the narrow widthportion 13 a of the resist pattern 13 is reduced. Accordingly, a failureor defect in the second electrode layers 9 b 2 and 9 c 2 is less likelyto occur even when the distance between the second and third busbars 9 band 9 c in the direction perpendicular or substantially perpendicular tothe lengthwise direction of the second and third busbars 9 b and 9 c isshortened. In addition, the failure or defect in the second electrodelayers 9 b 2 and 9 c 2 is less likely to occur even when the lengths ofthe second and third busbars 9 b and 9 c are increased. Accordingly,short-circuiting between the second busbar 9 b and the third busbar 9 cis also less likely to occur. Moreover, a further reduction in size ofthe duplexer 1 is able to be provided.

Referring to FIG. 1, in the duplexer 1, the lengths of the parallel armresonator P1 and the serial arm resonator S1 along the elastic-wavepropagating direction are larger than those of the serial arm resonatorsS2 to S4 along the elastic-wave propagating direction. Accordingly, thenumber of pairs of electrode fingers of the IDT electrode in each of theparallel arm resonator P1 and the serial arm resonator S1 is able to beincreased. As a result, filter characteristics, such as a Q value, areable to be improved. In this connection, a reduction in size of theduplexer 1 is able to be provided by arranging the parallel armresonator P1 and the serial arm resonator S1 adjacent to or in avicinity of each other in the direction perpendicular or substantiallyperpendicular to the elastic-wave propagating direction, as shown inFIG. 1. Furthermore, the distance between the parallel arm resonator P1and the serial arm resonator S1 in the direction perpendicular orsubstantially perpendicular to the elastic-wave propagating direction isable to be shortened even more. It is hence possible to improve thefilter characteristics, and to provide a further reduction in size ofthe duplexer 1.

The position at and the direction in which the second electrode layersof the second and third busbars 9 b and 9 c in the parallel armresonator P1 and the serial arm resonator S1 are each cut to bepartially separated are not particularly limited to the abovedescription. According to a modification of the first preferredembodiment, preferably only the second electrode layers of the secondand third busbars 9 b and 9 c are cut at positions opposing to eachother. The second and third busbars 9 b and 9 c may be cut in adirection other than the direction perpendicular or substantiallyperpendicular to the lengthwise direction, that is, a direction crossingthe lengthwise direction. Moreover, according to a modification of thefirst preferred embodiment, preferably only one of the second electrodelayers of the second and third busbars 9 b and 9 c is cut in at leastone location. Accordingly, the failure or defect in the second and thirdbusbars 9 b and 9 c is less likely to occur.

A duplexer including the same arrangement as the duplexer of the firstpreferred embodiment and a duplexer of a comparative example werefabricated, and insertion losses of first band pass filters in both ofthe duplexers were compared. The duplexer of the comparative exampleincludes a similar configuration as the duplexer of the first preferredembodiment except for that the former duplexer is not cut in portionscorresponding to the second electrode layers of the second and thirdbusbars.

Table 1, provided below, lists specifications of the IDT electrodes ofthe serial arm resonators S1 to S4, the parallel arm resonators P1 toP3, and the elastic wave resonators S11 and P11 in each of the duplexersaccording to the first preferred embodiment and the comparative example.Table 2, provided below, lists specifications of the IDT electrodes ofthe first and second longitudinally-coupled resonator-type elastic wavefilters 7 a and 7 b. Specifications of the reflectors are also listed inTables 1 and 2.

TABLE 1 IDT Electrode Reflector Number of Pairs Pitch of Number of Pitchof of Electrode Intersecting Electrode Electrode Electrode Fingers(pairs) Width (μm) Fingers (μm) Fingers Fingers (μm) Serial ArmResonator S1 82 78.35 5.5475 9 5.5687 Serial Arm Resonator S2 55 85.215.4568 3 5.5050 Serial Arm Resonator S3 64 186.25 5.5687 9 5.6189 SerialArm Resonator S4 51 114.22 5.5214 7 5.5390 Parallel Arm Resonator P1 113125.20 5.7303 9 5.7303 Parallel Arm Resonator P2 45 194.90 5.8004 95.8004 Parallel Arm Resonator P3 126 129.26 5.7568 9 5.7568 Elastic WaveResonator S11 108 60.08 5.1695 5 5.1695 Elastic Wave Resonator P11 2794.86 5.7316 5 5.7316

TABLE 2 Number of Pairs Number of Pitch of of Electrode ElectrodeElectrode Fingers in IDT Fingers in Intersecting Fingers Electrode(pairs) Reflector Width (μm) (μm) First IDT ELECTRODE 10Ba 8 — 116.325.3011 Longitudinally-Coupled IDT ELECTRODE 10Bb 23  — 116.32 5.3276Resonator-Type IDT ELECTRODE 10Bc 8 — 116.32 5.3011 Elastic Wave Filter7a Reflector 11B — 54 — 5.4151 Second IDT ELECTRODE 10Ca 8 — 121.705.3119 Longitudinally-Coupled IDT ELECTRODE 10Cb 28  — 121.70 5.3603Resonator-Type IDT ELECTRODE 10Cc 8 — 121.70 5.3119 Elastic Wave Filter7b Reflector 11C — 40 — 5.4613

FIG. 9 is a graph plotting insertion losses of the respective first bandpass filters in the first preferred embodiment and the comparativeexample. A solid line represents the result of the first preferredembodiment, and a broken line represents the result of the comparativeexample.

As seen from FIG. 9, the insertion loss of the first band pass filter inthe first preferred embodiment is equal or substantially equal to theinsertion loss of the first band pass filter in the comparative example.Thus, the first preferred embodiment is able to provide theabove-described advantageous effects without causing an insertion lossdue to diffraction of the elastic wave and an increase of electricalresistance.

Second Preferred Embodiment

FIG. 10 is a schematic plan view of an elastic wave device according toa second preferred embodiment of the present invention.

The elastic wave device according to the second preferred embodiment isa duplexer 21 shown in FIG. 10. The duplexer 21 is different from theduplexer 1 according to the first preferred embodiment in that each offirst and second band pass filters 23 a and 23 b includes first andsecond elastic wave elements. The duplexer 21 includes the same orsubstantially the same elements and features as the duplexer 1 accordingto the first preferred embodiment in the elements and features otherthan those described above.

More specifically, the parallel arm resonator P3 in the first band passfilter 23 a corresponds to the above-described first elastic waveelement, and the elastic wave resonator S11 in the second band passfilter 23 b corresponds to the above-described second elastic waveelement. The parallel arm resonator P3 and the elastic wave resonatorS11 are adjacent to or in a vicinity of each other in the directionperpendicular or substantially perpendicular to the elastic-wavepropagating direction. The parallel arm resonator P3 includes first andsecond busbars 29 a and 29 b that are opposed to each other. The elasticwave resonator S11 includes third and fourth busbars 29 c and 29 d thatare opposed to each other. The second busbar 29 b and the third busbar29 c extend parallel or substantially parallel to each other. The secondand third busbars 29 b and 29 c are arranged with a gap lefttherebetween in the direction perpendicular or substantiallyperpendicular to the lengthwise direction.

Each of the second and third busbars 29 b and 29 c includes a firstelectrode layer and a second electrode layer. At least a portion of thesecond electrode layer is laminated on the first electrode layer. Thesecond electrode layers of the second busbar 29 b and the third busbar29 c are cut, similar to the second and third busbars 9 b and 9 c in thefirst preferred embodiment. Thus, the second and third busbars 29 b and29 c include cut portions 29B and 29C, respectively.

The duplexer 21 is able to be manufactured similar to the manufacturingprocess of the duplexer 1 according to the first preferred embodiment.More specifically, the second and third busbars 29 b and 29 c are ableto be manufactured similar to the second and third busbars 9 b and 9 cin the parallel arm resonator P1 and the serial arm resonator S1. In thesecond preferred embodiment, therefore, a formation failure or defect inthe second and third busbars 29 b and 29 c in the parallel arm resonatorP3 and the elastic wave resonator S11 is less likely to occur inaddition to the advantageous effects of the first preferred embodiment.

Furthermore, the distance between the first band pass filter 23 a andthe second band pass filter 23 b is able to be shortened even more.Accordingly, the size of the duplexer 21 is able to be further reduced.

The preferred embodiments of present invention are able to be suitablyapplied to individual band pass filters as well without being limited toa duplexer. In addition, the preferred embodiments of present inventionare able to be suitably applied to, for example, a multiplexer includingthree or more band pass filters.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An elastic wave device comprising: apiezoelectric substrate; and a plurality of elastic wave elementsprovided on the piezoelectric substrate and including interdigitaltransducer (IDT) electrodes, respectively; wherein the plurality ofelastic wave elements includes a first elastic wave element and a secondelastic wave element; the IDT electrode of the first elastic waveelement includes first and second busbars that oppose each other, andthe IDT electrode of the second elastic wave element includes third andfourth busbars that oppose each other; the second busbar and the thirdbusbar extend parallel or substantially parallel to each other; a gap ispresent between the second busbar and the third busbar in a directionperpendicular or substantially perpendicular to an elastic-wavepropagating direction; each of the second and third busbars includes afirst electrode layer and a second electrode layer; at least a portionof the second electrode layer is laminated on the first electrode layer;the second electrode layer of the second busbar is cut in at least onelocation in a direction crossing the elastic-wave propagating direction;each of the IDT electrodes of the first and second elastic wave elementsincludes a plurality of electrode fingers that are respectivelyconnected to the second and third busbars; and a number of cuts in thesecond electrode layer of at least one of the second and third busbarsis less than a number of the plurality of electrode fingers that areconnected to the corresponding second or third busbar.
 2. The elasticwave device according to claim 1, wherein the second electrode layer ofthe second busbar is cut in a direction perpendicular or substantiallyperpendicular to the elastic-wave propagating direction.
 3. The elasticwave device according to claim 1, wherein the second electrode layer ofthe third busbar is cut in at least one location in a direction crossingthe elastic-wave propagating direction.
 4. The elastic wave deviceaccording to claim 3, wherein the second electrode layer of the thirdbusbar is cut in a direction perpendicular or substantiallyperpendicular to the elastic-wave propagating direction.
 5. The elasticwave device according to claim 3, wherein the second electrode layer ofthe third busbar is cut in a portion corresponding to an extension froma cut portion of the second electrode layer of the second busbar, theextension extending in a direction in which the second electrode layerof the second busbar is cut.
 6. The elastic wave device according to ofclaim 1, wherein the plurality of elastic wave elements includes one ormore serial arm resonators and a plurality of parallel arm resonators,and the first and second elastic wave elements are included in theplurality of parallel arm resonators.
 7. The elastic wave deviceaccording to claim 1, further comprising: a first band pass filter; anda second band pass filter; wherein a pass band of the second band passfilter is different from a pass band of the first band pass filter; andthe first band pass filter includes at least one of the first and secondelastic wave elements.
 8. The elastic wave device according to claim 7,wherein the first band pass filter includes one of the first and secondelastic wave elements, and the second band pass filter includes theother of the first and second elastic wave elements.
 9. The elastic wavedevice according to claim 7, wherein the plurality of elastic waveelements includes one or more serial arm resonators and a plurality ofparallel arm resonators; and the one or more serial arm resonators areconnected in series between an input terminal of the first band passfilter and an antenna terminal.
 10. The elastic wave device according toclaim 9, wherein the second band pass filter includes an output terminaland a plurality of elastic wave filters connected in series between theoutput terminal and the antenna terminal.
 11. The elastic wave deviceaccording to claim 1, wherein the plurality of elastic wave elementsincludes a plurality of serial arm resonators and a plurality ofparallel arm resonators; and at least one of the plurality of parallelarm resonators is connected between ground and a junction of two of theplurality of serial arm resonators.
 12. The elastic wave deviceaccording to claim 1, wherein the second electrode layer of the secondbusbar is cut in a direction crossing a lengthwise direction of thesecond busbar to provide a cut portion of the second busbar.
 13. Theelastic wave device according to claim 12, wherein the first electrodelayer of the second busbar is exposed in the cut portion of the secondbusbar.
 14. The elastic wave device according to claim 1, wherein thesecond electrode layer of the third busbar is cut in a directioncrossing a lengthwise direction of the third busbar to provide a cutportion of the third busbar.
 15. The elastic wave device according toclaim 14, wherein the first electrode layer of the third busbar isexposed in the cut portion of the third busbar.
 16. A method ofpreparing the elastic wave device according to claim 1, comprising:providing a first metal film on a piezoelectric substrate; patterningthe first metal film to provide a wiring layer; covering at least aportion of the wiring layer with a resist pattern; providing a secondmetal film on the piezoelectric substrate in at least a portion of thepiezoelectric substrate covered by the resist pattern and a portion ofthe piezoelectric substrate not covered with the resist pattern; andpeeling off the resist pattern.